The core problem at the police department was an intelligence division which not just has executed many tortures and assassinations but conducted a political plot as well. They have instigated subjects to commit a crime, but have also framed them to make a false confession.
Many ranking officers at the intelligence division have been so corrupted and so radicalized to cause a fundamental trouble in Japan.
Their deeds have been closely related to their necessity. If they are not needed, they should support radical activists to conduct terrors and the government will revise a view against them that they are needed. Moreover, the intelligence has run a political plot by their own to contain a discussion whether they are needed or not.
In Japan, the issue was that they were radicalized toward the left extremist, as their sympathizers took over an intelligence control and sought its political ideal. Although, there has been another group of the officers who had a motivation to control the politics for an expansion of their authority.
There are two highly corrupted groups in the police intelligence, one of which is a left extremist sympathizers and the other is authoritarian who is connected to the left group, but not directional that much, purely to take over the power. They actually consist of one group separated into two factions.
Their operation was progressed further to create an enemy for the public. They have hired members of the left extremist as assets, though those became old without successors. Then, this danger should go away as the time goes by, but it is not acceptable to them, because they are sympathizers and because they need the enemy to prove their necessity.
That was why they created some of the lone wolf extremists. They are appropriate targets for them as they are limited at the headcount and they are containable in nature. Additionally, some of them have definitely disturbed the society, which justifies an intelligence to hire many officials and to obtain more budgets.
Apparently, some of the lone wolves were manipulated by the intelligence to commit a crime and even a mass murder. In this case, the authority knew when and where the incident should occur, which is basically under their control. Some of those attacks have eventually killed many people, which is a less evil to them as they are needed after these actions.
As a matter of fact, the intelligence is an organization to conduct an assassination, therefore they less care for the human life originally. It is just a matter of the subject, not an issue of the life or death, which they can judge either necessary or unnecessary by their own established standard.
The Japanese police has another issue that their retired officers have maintained their authority even after leaving their position. None of them have been selected democratically or even by the politics, but the previous leader has decided their successor.
This is one of the reasons why the retired can still maintain the power, which implies once the strong director was so corrupted, their successors are just subordinated to him. This is also one of the main reasons why the police corruption could not cease, even though many Japanese people have realized they are so wrong.
As mentioned before, the Japanese police department hires 20-30 new grads every year for the directorate candidate. They eventually will become directors of the police department, so that the whole department is in danger when dozens of them have lost their mind. These dozens can deploy the whole police officers, which was why the police department has been changed to the criminal organization.
Although, not all the ordinal police officers are exempted from the crime activity. There are definitely some of them even to use an electromagnetic wave for their sake, which is not just a result of the corrupted ranking officers.